1. Field of the Invention
The present invention relates generally to semiconductor fabrication processes, and more particularly to an apparatus and method for removing particles from a surface.
2. Description of Related Art
Removal of sub-100 nanometer (nm) particles from a surface can be challenging for semiconductor fabrication processes. These particles may include contaminants on the surface including materials such as organic material, dust, residue, and/or metal impurities. Generally, the particles accumulate when a substrate is being stored or is in a stand-by state between successive processes and may cause defects, particularly for integrated circuits on a substrate.
The surface-particle interactions depend on the material and the surface structure. As such, the energy transfer efficiency needed to remove a particle from a surface strongly depends on the size of the particle on the surface. Generally, adhesive forces between the particle and the surface need to be broken and the particle needs to be transported far enough away from the surface such that the particle will not be redeposited on the surface.
Current methods for removing particles include wet cleaning techniques that involve immersing a substrate in a series of chemical solutions or spraying a series of chemical solutions onto a substrate, including for example, hydrofluoric acid, hydrogen peroxide solution, sulfuric acid, etc. In some techniques, a spin brush and/or a megasonic cleaner may be included. However, these processes are both expensive and produce waste that is environmentally harmful. Additionally, the use of a spin brush or an megasonic cleaner can be effective in removing large particles, but are hardly effective in removing particles on the order of submicrons or smaller.
Laser shockwave cleaning is another application using laser for surface cleaning. Particle removal efficiency depends on the momentum transferred to the particle on the surface, which in turn depends on the shock velocity parallel to the surface. The shock velocity depends on different parameters including the gas temperature and pressure. During the shock creation, plasma will form around the focus point of the laser light. However, when the focal point of the laser comes close to the surface, the plasma created can touch the surface and may cause damage to the surface.
Additionally, Next Generation Lithography (NGL) used in semiconductor technology includes reflective optics on glass substrates which have a surface roughness of approximately 1.5 Angstrom RMS or less to prevent scattering of the light, which may degrade the lithography process performance. Generally, all particles larger than about 27 nanometers need to be removed from the surface of a mask substrate that is used for NGL. The conventional wet cleaning techniques that use under etching of particles to remove particles from the surface are no longer applicable as they increase the surface roughness beyond the required value. In addition, most of the current advanced cleaning tools do not have the ability to remove the total particles with size of 27 nm and larger from the surface of the plates. This is due to the lack of a mechanism that is able to convey relatively high energy or momentum in distances of few nanometers from the surface. Further, current tools lack a mechanism to increase the population of reactive species in the vicinity of the interface. Most of the chemical reactions are driven by diffusion of the reactive species toward the surface.
The referenced shortcomings are not intended to be exhaustive, but rather are among many that tend to impair the effectiveness of previously known techniques concerning particle removal; however, those mentioned here are sufficient to demonstrate that the methodologies appearing in the art have not been satisfactory and that a significant need exists for the techniques described and claimed in this disclosure.